I would recomend a distel as the next step from a prusik, its easier to tie, and safer as it has both legs on the karabiner.

After that then maybe a helical or VT.

The helical can be used a bit like a prussik as it can be shoved up the rope in the same way, but really it is meant as a self advancing hitch to be used with the same method as a vt, i.e. without the body thrust technique associated with the prussik.

The distel is a very safe way to learn this new method before moving on to the more tempermantal knots like the helical and vt.

IMO.